Headset or headphone listening is becoming increasingly popular, for instance because of to the increasing penetration of portable audio players such as MP3 players into the consumer market. Even mobile phones nowadays allow audio playback, e.g. music playback, on stereo headphones.
Another noticeable trend is the growing use of Active Noise Reduction (ANR) headphones, which attempt to isolate the user from the ambient sounds such as car or aircraft engine noise, fan noise, traffic noise and so on, by means of anti-sound played through the headphone loudspeakers. The anti-sound is calculated from microphones placed on (so-called feed-forward ANR) or inside (so-called feed-back ANR) the headphone.
The feed-back ANR configuration is particularly interesting as the microphone is not only capable of capturing external noise that penetrates the earpiece as well as the audio signals that are being played back by the earpiece loudspeakers, but is also capable of recording sounds that emanate from the user's body, such as breathing and heart rhythm. This works especially well when the earpiece is tightly fitted into the ear.
A usual problem encountered while using any type of stereo headset is the need to respect the left/right order, i.e. ensuring that the correct earpiece is placed in or on the correct ear. A left/right inversion is not dramatic in case of music listening, but in case of movie playback and augmented reality systems such as auditory displays, a left/right inversion has a negative impact on the overall experience because in these situations, a correlation exists between the sounds played over the earpieces and the physical location of the user or the directionality of events such as moving images on a movie screen to which the sounds relate.
Although most headsets are marked with a “L” on the left earpiece and a “R” on the right earpiece, the user may choose to ignore these indications, which can lead to the earpieces being placed in or on the incorrect ear. Some other conventions exist to help the user place the correct earpiece in or on the correct ear, such as asymmetric design features, e.g. a cable plug on the left side only for full-size headphones or a shorter cable portion on the left side for in-ear headphones. However, these measures do not prevent the user from ignoring these design features.